Pregnancy and Luteal Responses to Embryo Reinsertion following Embryo Flushing in Donor Mares.
Authors: Martínez-Boví Rebeca, Gaber Jana T H, Sala-Ayala Laura, Plaza-Dávila María, Cuervo-Arango Juan
Journal: Animals : an open access journal from MDPI
Summary
# Editorial Summary: Embryo Reinsertion and Luteal Function in Donor Mares Embryo transfer programmes commonly involve flushing the uterus to recover embryos, yet whether reinserting the embryo into the same donor mare immediately after collection affects pregnancy rates and ovarian function remains unclear. Martínez-Bové and colleagues conducted two experiments using 20 mares across 49 cycles, comparing pregnancy outcomes and progesterone profiles when donor mares received their own embryos back (EF-ET group) versus when non-inseminated recipient mares received Day 8 embryos (ET group), with and without a secondary flushing procedure. Reinsertion into donor mares yielded dramatically inferior pregnancy rates—0% in the immediate reinsertion protocol versus 75% in recipients—whilst progesterone concentrations dropped significantly 72 hours post-reinsertion, indicating premature luteolysis in three animals who developed endometritis. The second experiment revealed that embryos recovered from donors subjected to reinsertion and reflushing showed markedly poorer quality (57% were graded 3–4 with degeneration versus none in the ET group) and bacterial contamination was evident in embryo flushes from both protocols, suggesting procedural trauma and infection compromise embryo viability and endometrial health. For practitioners, these findings indicate that reinserting embryos into donor mares offers no advantage over conventional recipient transfer and may cause iatrogenic endometrial inflammation and luteal failure, arguing strongly against this practice in commercial embryo transfer programmes.
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Practical Takeaways
- •Returning flushed embryos to donor mares immediately after collection is contraindicated—the procedure causes luteal dysfunction, endometritis, and complete pregnancy failure in this study population
- •Embryo flushing itself may damage embryos regardless of reinsertion strategy; embryos showed significantly higher degeneration rates when collected 24 hours post-transfer compared to day 8 collection
- •Use recipient mares for embryo transfer rather than attempting same-mare reinsertion to maximize pregnancy success rates (75% vs 0%)
Key Findings
- •Embryo reinsertion in donor mares (EF-ET) resulted in 0% pregnancy rate compared to 75% in recipient mares (ET group) in Experiment 1
- •Progesterone concentration decreased significantly 72 hours after EF-ET (p=0.05) but not in EF or ET groups, with three mares showing full luteolysis and endometritis signs
- •In Experiment 2, more grade 1 embryos were recovered from ET cycles (5/6) versus EF-ET cycles (3/7), with 4 degenerated embryos (grade 3-4) only in EF-ET group
- •Bacterial contamination and embryo capsule fragments were detected in both EF-ET and ET groups, suggesting embryonic damage during the flushing procedure